Well, I spent the last few days burning in my HA-RX900s for the majority of each day plugged into a radio, turned up loud, and put under a pile of blankets. They're somewhere between 100 and 125 hours, I'd guess. Enough to take them out now and make some more definitive judgments, at least.

I have to say that these headphones are no joke. An extremely good value for the money, and I don't imagine that anybody would miss their money if they picked up a pair. My assessments are pretty much on par with what has already been noticed; to summarize:

Soundstage:
Very strong soundstage. Although I think the soundstage on my DT-880s extends further sideways, it can be fairly 2-dimensional. The soundstage on the RX900s, however, seems to spread around in a way that the Beyers just don't recreate; it sort of envelops my head more. It is nowhere near as refined as the soundstage on the DT-880s, lacking the "airiness" that make the Beyers my favorite phones, but it does provide a very strong, defined placement of individual instruments/voices in a 3-dimensional plane.

Bass and midrange:
The lowest of notes is where the RX-900s may, in fact, trump the Beyers, believe it or not. Bass is tight, and goes quite deep. Kick drums are not quite as snappy as on my MS-1s, but there is enough punch there to keep me very satisfied. However, it is in this strength of these phones where I also find their biggest fault (in my opinion): there is a midbass hump, windowed somewhere around 125-250 Hz (in my best guess), which colors much of the midrange, or at least recesses it by comparison to the point that it lacks prominence. Bass notes in this region begin to lose their tightness and become difficult to place in the soundstage. When eq-ed to compensate for this hump, the midrange opens up surprisingly well. I believe this is where the problem lies related to the recessed vocals that some have noticed with these phones. I would be extremely interested in trying to see if there is a way to mod them to get rid of (or, at least, lower) this midbass hump, as I can't have the eq on all the time on my dedicated music PC.

High midrange and treble:
Treble notes are not the strongest suit for these headphones, but I'm always trying to keep in mind that these only cost me $68. Not as extended as the Beyers, yet not as aggressive as the Alessandros. There is a slight edginess on some tracks with cymbols and higher guitar notes, however, this seems to reduce with burn-in. As I already noted, the midrange (including the higher midrange, i.e. female vocals) would open up significantly if a way could be found to reduce the midbass hump that seems to congest the rest of the spectrum. If this could be done, I'm fairly certain that these headphones would be taken more seriously, and would be strong contenders with other, more established, headphones.

Comfort:
Very comfy, yet fairly warm. This is my first set of closed phones, so I'm not completely sure, but I'm guessing that the heat comes with the territory. I can't listen for more than an hour without my ears becoming uncomfortable from the heat. The pads are wonderful, though, and cushion very well. The clamping force could be taken down a couple of notches for my head, however, but your mileage may vary.

Ultimately, though, I think that these phones are a good value because I keep wanting to reach for them. I've already purchased another headphone stand (a.k.a. Walmart wooden banana hook with the metal hook sawed off!) to match the others, and the JVCs are sitting well with Beyers and Alessandros. The music is accurate enough, but most important fun enough, to keep me wanting to listen to more, and I'd have to say that I wouldn't be the saddest person in the world if these were the only headphones I owned. Granted... I'd miss my Beyers and Alessandros... but I wouldn't feel that my listening experience would be missing something huge...

Very good! Been wanting to review my 700's but haven't had time to really audition them properly, but most of my findings are the same as mine, minus the ample soundstage. Considering I wanted more intense "Rock" can, that's fine by me.
The clamping was easily corrected by manually bending the headband and shouting "Hulk angry, Hulk smash!" and the discomfort was mostly gone.
I can't complain so much for the heat, but I'm in the mid-west in Nov. so it's welcome. Let's see what I think come July.
Definitely impressive for the cash.
Thanks for the impressions.

Very good! Been wanting to review my 700's but haven't had time to really audition them properly, but most of my findings are the same as mine, minus the ample soundstage. Considering I wanted more intense "Rock" can, that's fine by me.
The clamping was easily corrected by manually bending the headband and shouting "Hulk angry, Hulk smash!" and the discomfort was mostly gone.
I can't complain so much for the heat, but I'm in the mid-west in Nov. so it's welcome. Let's see what I think come July.
Definitely impressive for the cash.
Thanks for the impressions.

I'd like to hear your review of the 700's. Im thinking of either picking up the 700's or 900's in a little but but I'm having trouble deciding. The music I listen to is mostly hard rock / metal so how do you think those would be for that? And does anyone know how the 900s are for metal? My only other headphone is a pair of SR60s so do you guys think these would be a step above or below them? I was thinking that maybe the 900s would be better because theyre so different from the grados but I dont know if that would be necessarily better for metal. Thanks.

Nice review, only thing I really disagree with is the soundstage as well, it is wide but it doesn't seem to be that 3D (maybe your amp helps?), however I agree that it has very nice instrument placement and seperation. In live recordings the vocals may seem to come ahead and to the right of me which is neat. But I see that you have a pretty good amp, I was wondering what kind of improvements do you see when you amp your JVC HA-RX 900s?

Nice review, only thing I really disagree with is the soundstage as well, it is wide but it doesn't seem to be that 3D (maybe your amp helps?), however I agree that it has very nice instrument placement and seperation. In live recordings the vocals may seem to come ahead and to the right of me which is neat. But I see that you have a pretty good amp, I was wondering what kind of improvements do you see when you amp your JVC HA-RX 900s?

I really do think that the amp helps quite a bit. The only other way I've tried them is with my portable amp, which is a Leckerton UHA-3. It's got enough juice, but I notice two things when I switch to the non-portable setup: 1) bass is both deeper and tighter, and 2) the soundstage is slightly larger in all dimensions, and imaging is more precise. Furthermore, I believe that the JVCs benefit more from this jump than my Beyers. This isn't to say that they surpass the Beyers, only that they seem to benefit slightly more from better upstream components.

However, this could be to the upgrade in source as well (i.e. internal DAC in the Leckerton vs. external Keces), but I'd imagine that the combination of the better DAC and better amp work together to create a more cohesive presentation in the overall sound.

i want the rx900 because the pads look amazing. but i dont have enough money
i only have the patience to raise enough money for the rx700. Which is better for hip hop and electronic? Are both the rx700 and 900 closed?